In general, the core member to be used in a vacuum insulator has a small heat conduction rate, and inorganic chemical compounds generating little gas are suitable for this core member. The vacuum insulator employing a glass-fiber laminated unit, among others, as the core member is excellent in heat insulating performance. An example of such core member is disclosed in Examined Japanese Patent Publication No. H07-103955 (hereinafter referred to as Patent Document 1). FIG. 8 schematically shows a cross sectional view of the core member disclosed in Patent Document 1.
As shown in FIG. 8, inorganic thin fibers 101a (hereinafter referred to as fiber 101a) such as glass fiber are laminated one after the other such that their longitudinal direction becomes vertical with respect to the heat transfer direction of the vacuum insulator. On top of that, fibers 101a are laminated at random such that they cross with each other in longitudinal direction and make point contacts between them. Penetration fibers 101c (hereinafter referred to as fiber 101c) are inserted such that they run in parallel with the heat transfer direction. Inorganic thin fiber mat 101d is thus formed. A plurality (N sheets) of inorganic thin fiber mats 101d are piled up, thereby forming core member 101. Core member 101 is mounted to jacket (not shown) made of stainless steel, whereby the vacuum insulator is completed.